In 3rd generation partnership project (3GPP) standardization, a multitude of different access systems are being specified that lead to a situation where mobile network operator (MNO) networks consist of different cell types: different access network generations, such as 2G, 3G, high-speed packet access (HSPA), and long-term evolution (LTE); different carriers inside each access network generation; and different cell size (e.g. macro, pico, femto). A network consisting of different cell types is usually referred to as a heterogeneous network (HetNet). Under HetNet work items, 3GPP radio access network (RAN) groups are working on solutions e.g. to cope with interference issues that femto cells may cause in a macro cell environment.
HetNets having several different radio access technologies (RATs) with overlapping coverage requires new traffic management mechanisms and allows for optimization of network efficiency and user experience. Such scenario is expected especially in dense populated areas, e.g. cities.
In addition, to cope with the huge increase of data traffic, 3GPP release 10 has defined mechanisms to offload traffic from a MNO's core network. A solution to bypass MNO's core network with subscriber data traffic is attracting interest from manufacturers and operators. Currently, a work item for local internet protocol (IP) access (LIPA) and selected IP traffic offload (SIPTO) has been established and a SIPTO solution for release 10 with local gateway (GW) selection has been selected. Via this local GW all traffic of selected subscribers and directed to selected destinations (e.g. to the Internet) can be offloaded from the mobile operators network. With the LIPA feature traffic directed to a local home or enterprise network can directly access these networks without traversing the operator's core network. (This feature is defined in 3GPP release 10 for home-cells/home networks only.)
The SIPTO feature is intended to differentiate subscribers' IP traffic so that a certain amount of IP traffic to/from IP devices connected to the cellular network or to a home based network (HNB) is forwarded on the shortest path out of the MNO's network, especially internet bulk data traffic to the internet.
The RAN has a possibility to steer traffic, for example to allow equally loaded cells by redirection or to handover subscribers e.g. from a macro cell to a pico cell in a hot spot. The target is efficient utilization of network resources and high user experience. For this procedure RAN specific criteria and algorithms are used, taking into account e.g. load of a cell and signal strength.
It would further enhance the efficiency of the algorithms if it was possible to take subscriber specific attributes into account. For example, it does not make sense to handover—for load balancing reasons—a subscriber that is consuming only very little radio resources, especially because also handover procedures as such require signaling resources from the network. However, due to the function split between radio and core network, this information is not available in the RAN. The reason is that the RAN should not be loaded with tasks like storing subscriber information.
One possibility would be that the core network would, in the process of establishing radio bearers, add additional information about subscribers to the relevant signaling messages, e.g. that this is a flat rate subscriber, or some categories like gold/silver subscribers. But this would require enhancing the RAN—core network interface (Iu, S1), storing the subscriber information per bearer context and it would also violate the RAN—core function split.
In 3GPP release 8, a mechanism is defined (RFSP=RAT/Frequency Selection Index) that allows to distribute subscribers (e.g. according to terminal capabilities) across different RATs. This allows some global balancing of the operators' subscribers to the available bandwidths distributed over different RATs and different carriers. However, there is no further intelligence defined for RAT and cell selection to take into account other subscriber characteristics in combination with dynamic load situations in cells.
Thus, there is a need to find a more simple solution, also to allow implementation in near term to solve current challenges.